Validation of spermidine synthase as a drug target in African trypanosomes

Martin C Tayor , Harparkash Kaur , Bernard Blessington , John M Kelly , Shane R Wilkinson (1)

1 School of Biological and Chemical Science

The trypanocidal activity of the ornithine decarboxylase (ODC) inhibitor difluoromethylornithine (DFMO) has validated polyamine biosynthesis as a target for chemotherapy. As DFMO is one of only two drugs used to treat patients with late-stage African trypanosomasis, the requirement for additional drug targets is paramount. Here we report the biochemical properties of Trypanosoma brucei spermidine synthase (TbSpSyn), the enzyme immediately down-stream of ODC in this pathway. Recombinant TbSpSyn was purified and shown to catalyse the formation of spermidine from putrescine and decarboxylated S-adenosylmethionine. To determine the functional importance of TbSpSyn in bloodstream form parasites, we used a tetracycline-inducible RNA interference (RNAi) system. Down-regulation of the corresponding mRNA correlated with a decrease in intracellular spermidine and cessation of growth. This phenotype could be complemented by expressing the spermidine synthase gene from Leishmania major in cells undergoing RNAi, but could not be rescued by addition of spermidine to the medium due to the lack of a spermidine uptake capacity. These data therefore genetically validate TbSpSyn as a target for drug development and indicate that in the absence of a functional biosynthetic pathway, bloodstream form T. brucei cannot scavenge sufficient spermidine from their environment to meet growth requirements.

Mots clés: Life Sciences

Martin C Tayor, Harparkash Kaur, Bernard Blessington, John M Kelly, Shane R Wilkinson. Validation of spermidine synthase as a drug target in African trypanosomes. Biochemical Journal, 2007, 409 (2), pp.563-569. ⟨10.1042/BJ20071185⟩. ⟨hal-00478880⟩